The biogenesis of chloroplast organelle has been described in great detail. However, a description of the transcriptional activity of this DNA is missing, and very little is known about the transcriptional regulation of organelle gene expression. The research proposed will concentrate on the determination of spatial and temporal organization of organelle genes. Using synchronously grown cultures and Y1 mutants of C. reinhardi, total RNA was isolated and hybridized to restriction fragments of chloroplast DNA. Southern blot technique was used for identification of the transcriptionally active fragments during the cell cycle and chloroplast development. Three types of fragment have been identified: a) fragments whih are transcribed at any stage of cell cycle and development. These fragments contain genes which are expressed for most of the cell life; b) fragments which are expressed only at specific stages of the cell cycle or chloroplast development. Particularly interesting fragments in this class are those expressed at early stages of the cell cycle and development (early genes); and c) fragments which are never expressed in vivo. The attempt to demonstrate their expression in vitro also showed that existing polymerases do not recognize initiation signals on these fragments. The Hart system was also used for identification of proteins encoded in chloroplast DNA. 5 30S ribosomal proteins and 6 non-ribosomal proteins were identified as encoded in this DNA.